I dont know if there is a specific gender only blood test, but there is the NIPT. It is specifically for chromosonal issues, but can also tell you the gender if wanted. It can only be done from 10 weeks onwards though, expensive and only privately. If there is a gender only test, it would likely be cheaper.

I paid for the NIPT as high risk due to my age (38 at the time) and it showed a chromosonal abnormality. We also found out the gender, but that was optional.